diff --git a/ports/cc3200/hal/cc3200_hal.c b/ports/cc3200/hal/cc3200_hal.c
index 56dd2b2b8..8bfd2fda1 100644
--- a/ports/cc3200/hal/cc3200_hal.c
+++ b/ports/cc3200/hal/cc3200_hal.c
@@ -140,10 +140,15 @@ void mp_hal_delay_ms(mp_uint_t delay) {
     }
 }
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
-    mp_os_dupterm_tx_strn(str, len);
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
+    mp_uint_t ret = len;
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        ret = dupterm_res;
+    }
     // and also to telnet
     telnet_tx_strn(str, len);
+    return ret;
 }
 
 int mp_hal_stdin_rx_chr(void) {
diff --git a/ports/esp32/mphalport.c b/ports/esp32/mphalport.c
index 8e14bda59..fb322dff6 100644
--- a/ports/esp32/mphalport.c
+++ b/ports/esp32/mphalport.c
@@ -125,24 +125,34 @@ int mp_hal_stdin_rx_chr(void) {
     }
 }
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
     // Only release the GIL if many characters are being sent
+    mp_uint_t ret = len;
+    bool did_write = false;
     bool release_gil = len > 20;
     if (release_gil) {
         MP_THREAD_GIL_EXIT();
     }
     #if CONFIG_ESP_CONSOLE_USB_SERIAL_JTAG
     usb_serial_jtag_tx_strn(str, len);
+    did_write = true;
     #elif CONFIG_USB_OTG_SUPPORTED
     usb_tx_strn(str, len);
+    did_write = true;
     #endif
     #if MICROPY_HW_ENABLE_UART_REPL
     uart_stdout_tx_strn(str, len);
+    did_write = true;
     #endif
     if (release_gil) {
         MP_THREAD_GIL_ENTER();
     }
-    mp_os_dupterm_tx_strn(str, len);
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        did_write = true;
+        ret = MIN((mp_uint_t)dupterm_res, ret);
+    }
+    return did_write ? ret : 0;
 }
 
 uint32_t mp_hal_ticks_ms(void) {
diff --git a/ports/esp8266/esp_mphal.c b/ports/esp8266/esp_mphal.c
index 394c9796c..6f158058d 100644
--- a/ports/esp8266/esp_mphal.c
+++ b/ports/esp8266/esp_mphal.c
@@ -94,8 +94,14 @@ void mp_hal_debug_str(const char *str) {
 }
 #endif
 
-void mp_hal_stdout_tx_strn(const char *str, uint32_t len) {
-    mp_os_dupterm_tx_strn(str, len);
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, uint32_t len) {
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res < 0) {
+        // no outputs, nothing was written
+        return 0;
+    } else {
+        return dupterm_res;
+    }
 }
 
 void mp_hal_debug_tx_strn_cooked(void *env, const char *str, uint32_t len) {
diff --git a/ports/mimxrt/mphalport.c b/ports/mimxrt/mphalport.c
index 2114baaae..be4b1d8b5 100644
--- a/ports/mimxrt/mphalport.c
+++ b/ports/mimxrt/mphalport.c
@@ -112,9 +112,12 @@ int mp_hal_stdin_rx_chr(void) {
     }
 }
 
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    mp_uint_t ret = len;
+    bool did_write = false;
     if (tud_cdc_connected()) {
-        for (size_t i = 0; i < len;) {
+        size_t i = 0;
+        while (i < len) {
             uint32_t n = len - i;
             if (n > CFG_TUD_CDC_EP_BUFSIZE) {
                 n = CFG_TUD_CDC_EP_BUFSIZE;
@@ -125,6 +128,7 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
                 MICROPY_EVENT_POLL_HOOK
             }
             if (ticks_us64() >= timeout) {
+                ret = i;
                 break;
             }
 
@@ -132,10 +136,17 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
             tud_cdc_write_flush();
             i += n2;
         }
+        did_write = true;
+        ret = MIN(i, ret);
     }
     #if MICROPY_PY_OS_DUPTERM
-    mp_os_dupterm_tx_strn(str, len);
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        did_write = true;
+        ret = MIN((mp_uint_t)dupterm_res, ret);
+    }
     #endif
+    return did_write ? ret : 0;
 }
 
 uint64_t mp_hal_time_ns(void) {
diff --git a/ports/minimal/uart_core.c b/ports/minimal/uart_core.c
index c7af24404..a3dfe697e 100644
--- a/ports/minimal/uart_core.c
+++ b/ports/minimal/uart_core.c
@@ -29,10 +29,14 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 // Send string of given length
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    mp_uint_t ret = len;
     #if MICROPY_MIN_USE_STDOUT
     int r = write(STDOUT_FILENO, str, len);
-    (void)r;
+    if (r >= 0) {
+        // in case of an error in the syscall, report no bytes written
+        ret = 0;
+    }
     #elif MICROPY_MIN_USE_STM32_MCU
     while (len--) {
         // wait for TXE
@@ -41,4 +45,5 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
         USART1->DR = *str++;
     }
     #endif
+    return ret;
 }
diff --git a/ports/nrf/drivers/bluetooth/ble_uart.c b/ports/nrf/drivers/bluetooth/ble_uart.c
index 320657370..4ea811572 100644
--- a/ports/nrf/drivers/bluetooth/ble_uart.c
+++ b/ports/nrf/drivers/bluetooth/ble_uart.c
@@ -110,10 +110,11 @@ int mp_hal_stdin_rx_chr(void) {
     return (int)byte;
 }
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
     // Not connected: drop output
-    if (!ble_uart_enabled()) return;
+    if (!ble_uart_enabled()) return 0;
 
+    mp_uint_t ret = len;
     uint8_t *buf = (uint8_t *)str;
     size_t send_len;
 
@@ -134,6 +135,7 @@ void mp_hal_stdout_tx_strn(const char *str, size_t len) {
         len -= send_len;
         buf += send_len;
     }
+    return ret;
 }
 
 void ble_uart_tx_char(char c) {
diff --git a/ports/nrf/drivers/usb/usb_cdc.c b/ports/nrf/drivers/usb/usb_cdc.c
index e33a42548..3ca2acbf3 100644
--- a/ports/nrf/drivers/usb/usb_cdc.c
+++ b/ports/nrf/drivers/usb/usb_cdc.c
@@ -231,12 +231,12 @@ int mp_hal_stdin_rx_chr(void) {
     return 0;
 }
 
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
-
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
     for (const char *top = str + len; str < top; str++) {
         ringbuf_put((ringbuf_t*)&tx_ringbuf, *str);
         usb_cdc_loop();
     }
+    return len;
 }
 
 void mp_hal_stdout_tx_strn_cooked(const char *str, mp_uint_t len) {
diff --git a/ports/nrf/mphalport.c b/ports/nrf/mphalport.c
index f6c934a8b..c964a26c2 100644
--- a/ports/nrf/mphalport.c
+++ b/ports/nrf/mphalport.c
@@ -196,10 +196,12 @@ int mp_hal_stdin_rx_chr(void) {
     return 0;
 }
 
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
     if (MP_STATE_VM(dupterm_objs[0]) != MP_OBJ_NULL) {
         uart_tx_strn(MP_STATE_VM(dupterm_objs[0]), str, len);
+        return len;
     }
+    return 0;
 }
 
 void mp_hal_stdout_tx_strn_cooked(const char *str, mp_uint_t len) {
diff --git a/ports/pic16bit/pic16bit_mphal.c b/ports/pic16bit/pic16bit_mphal.c
index b2c80ba1b..f58abf783 100644
--- a/ports/pic16bit/pic16bit_mphal.c
+++ b/ports/pic16bit/pic16bit_mphal.c
@@ -75,10 +75,12 @@ void mp_hal_stdout_tx_str(const char *str) {
     mp_hal_stdout_tx_strn(str, strlen(str));
 }
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
+    mp_uint_t ret = len;
     for (; len > 0; --len) {
         uart_tx_char(*str++);
     }
+    return ret;
 }
 
 void mp_hal_stdout_tx_strn_cooked(const char *str, size_t len) {
diff --git a/ports/powerpc/uart_lpc_serial.c b/ports/powerpc/uart_lpc_serial.c
index 760615041..405bf2d1e 100644
--- a/ports/powerpc/uart_lpc_serial.c
+++ b/ports/powerpc/uart_lpc_serial.c
@@ -108,7 +108,7 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
     int i;
     for (i = 0; i < len; i++) {
         while (lpc_uart_tx_full()) {
@@ -116,4 +116,5 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
         }
         lpc_uart_reg_write(REG_RBR, str[i]);
     }
+    return len;
 }
diff --git a/ports/powerpc/uart_potato.c b/ports/powerpc/uart_potato.c
index 29f21934d..089e4e2be 100644
--- a/ports/powerpc/uart_potato.c
+++ b/ports/powerpc/uart_potato.c
@@ -118,7 +118,7 @@ int mp_hal_stdin_rx_chr(void) {
     return (char)(val & 0x000000ff);
 }
 
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
     int i;
 
     for (i = 0; i < len; i++) {
@@ -129,4 +129,5 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
         }
         potato_uart_reg_write(POTATO_CONSOLE_TX, val);
     }
+    return len;
 }
diff --git a/ports/renesas-ra/mphalport.c b/ports/renesas-ra/mphalport.c
index 91705129c..8a8bfd8dc 100644
--- a/ports/renesas-ra/mphalport.c
+++ b/ports/renesas-ra/mphalport.c
@@ -154,16 +154,20 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 // Send string of given length
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    mp_uint_t ret = len;
+    bool did_write = false;
     #if MICROPY_HW_ENABLE_UART_REPL
     if (MP_STATE_PORT(pyb_stdio_uart) != NULL) {
         uart_tx_strn(MP_STATE_PORT(pyb_stdio_uart), str, len);
+        did_write = true;
     }
     #endif
 
     #if MICROPY_HW_USB_CDC
     if (tud_cdc_connected()) {
-        for (size_t i = 0; i < len;) {
+        size_t i = 0;
+        while (i < len) {
             uint32_t n = len - i;
             if (n > CFG_TUD_CDC_EP_BUFSIZE) {
                 n = CFG_TUD_CDC_EP_BUFSIZE;
@@ -180,12 +184,20 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
             tud_cdc_write_flush();
             i += n2;
         }
+        ret = MIN(i, ret);
+        did_write = true;
     }
     #endif
 
     #if MICROPY_PY_OS_DUPTERM
-    mp_os_dupterm_tx_strn(str, len);
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        did_write = true;
+        ret = MIN((mp_uint_t)dupterm_res, ret);
+    }
     #endif
+
+    return did_write ? ret : 0;
 }
 
 void mp_hal_ticks_cpu_enable(void) {
diff --git a/ports/rp2/mphalport.c b/ports/rp2/mphalport.c
index 1c784fd73..c5ae221e9 100644
--- a/ports/rp2/mphalport.c
+++ b/ports/rp2/mphalport.c
@@ -151,14 +151,18 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 // Send string of given length
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    mp_uint_t ret = len;
+    bool did_write = false;
     #if MICROPY_HW_ENABLE_UART_REPL
     mp_uart_write_strn(str, len);
+    did_write = true;
     #endif
 
     #if MICROPY_HW_USB_CDC
     if (tud_cdc_connected()) {
-        for (size_t i = 0; i < len;) {
+        size_t i = 0;
+        while (i < len) {
             uint32_t n = len - i;
             if (n > CFG_TUD_CDC_EP_BUFSIZE) {
                 n = CFG_TUD_CDC_EP_BUFSIZE;
@@ -173,18 +177,26 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
                 mp_usbd_task();
             }
             if (timeout >= MICROPY_HW_USB_CDC_TX_TIMEOUT) {
+                ret = i;
                 break;
             }
             uint32_t n2 = tud_cdc_write(str + i, n);
             tud_cdc_write_flush();
             i += n2;
         }
+        ret = MIN(i, ret);
+        did_write = true;
     }
     #endif
 
     #if MICROPY_PY_OS_DUPTERM
-    mp_os_dupterm_tx_strn(str, len);
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        did_write = true;
+        ret = MIN((mp_uint_t)dupterm_res, ret);
+    }
     #endif
+    return did_write ? ret : 0;
 }
 
 void mp_hal_delay_ms(mp_uint_t ms) {
diff --git a/ports/samd/mphalport.c b/ports/samd/mphalport.c
index 3c803403f..de1650c99 100644
--- a/ports/samd/mphalport.c
+++ b/ports/samd/mphalport.c
@@ -200,9 +200,12 @@ int mp_hal_stdin_rx_chr(void) {
     }
 }
 
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    mp_uint_t ret = len;
+    bool did_write = false;
     if (tud_cdc_connected()) {
-        for (size_t i = 0; i < len;) {
+        size_t i = 0;
+        while (i < len) {
             uint32_t n = len - i;
             if (n > CFG_TUD_CDC_EP_BUFSIZE) {
                 n = CFG_TUD_CDC_EP_BUFSIZE;
@@ -213,14 +216,22 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
                 MICROPY_EVENT_POLL_HOOK_WITH_USB;
             }
             if (timeout >= MICROPY_HW_USB_CDC_TX_TIMEOUT) {
+                ret = i;
                 break;
             }
             uint32_t n2 = tud_cdc_write(str + i, n);
             tud_cdc_write_flush();
             i += n2;
         }
+        ret = MIN(i, ret);
+        did_write = true;
     }
     #if MICROPY_PY_OS_DUPTERM
-    mp_os_dupterm_tx_strn(str, len);
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        did_write = true;
+        ret = MIN((mp_uint_t)dupterm_res, ret);
+    }
     #endif
+    return did_write ? ret : 0;
 }
diff --git a/ports/stm32/mphalport.c b/ports/stm32/mphalport.c
index f8a5d66fc..dfd50cebd 100644
--- a/ports/stm32/mphalport.c
+++ b/ports/stm32/mphalport.c
@@ -57,14 +57,22 @@ MP_WEAK int mp_hal_stdin_rx_chr(void) {
     }
 }
 
-MP_WEAK void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+MP_WEAK mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
+    mp_uint_t ret = len;
+    bool did_write = false;
     if (MP_STATE_PORT(pyb_stdio_uart) != NULL) {
         uart_tx_strn(MP_STATE_PORT(pyb_stdio_uart), str, len);
+        did_write = true;
     }
     #if 0 && defined(USE_HOST_MODE) && MICROPY_HW_HAS_LCD
     lcd_print_strn(str, len);
     #endif
-    mp_os_dupterm_tx_strn(str, len);
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        did_write = true;
+        ret = MIN((mp_uint_t)dupterm_res, ret);
+    }
+    return did_write ? ret : 0;
 }
 
 #if __CORTEX_M >= 0x03
diff --git a/ports/unix/unix_mphal.c b/ports/unix/unix_mphal.c
index 8d6539c88..24c0fa3cd 100644
--- a/ports/unix/unix_mphal.c
+++ b/ports/unix/unix_mphal.c
@@ -184,10 +184,15 @@ main_term:;
     return c;
 }
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
     ssize_t ret;
     MP_HAL_RETRY_SYSCALL(ret, write(STDOUT_FILENO, str, len), {});
-    mp_os_dupterm_tx_strn(str, len);
+    mp_uint_t written = ret < 0 ? 0 : ret;
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        written = MIN((mp_uint_t)dupterm_res, written);
+    }
+    return written;
 }
 
 // cooked is same as uncooked because the terminal does some postprocessing
diff --git a/ports/webassembly/mphalport.c b/ports/webassembly/mphalport.c
index c938a6392..f91a50901 100644
--- a/ports/webassembly/mphalport.c
+++ b/ports/webassembly/mphalport.c
@@ -27,8 +27,9 @@
 #include "library.h"
 #include "mphalport.h"
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
     mp_js_write(str, len);
+    return len;
 }
 
 void mp_hal_delay_ms(mp_uint_t ms) {
diff --git a/ports/webassembly/mphalport.h b/ports/webassembly/mphalport.h
index 89efee697..1b3179698 100644
--- a/ports/webassembly/mphalport.h
+++ b/ports/webassembly/mphalport.h
@@ -28,7 +28,7 @@
 #include "shared/runtime/interrupt_char.h"
 
 #define mp_hal_stdin_rx_chr() (0)
-void mp_hal_stdout_tx_strn(const char *str, size_t len);
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len);
 
 void mp_hal_delay_ms(mp_uint_t ms);
 void mp_hal_delay_us(mp_uint_t us);
diff --git a/ports/windows/windows_mphal.c b/ports/windows/windows_mphal.c
index d1bbb931a..f88491707 100644
--- a/ports/windows/windows_mphal.c
+++ b/ports/windows/windows_mphal.c
@@ -221,10 +221,11 @@ int mp_hal_stdin_rx_chr(void) {
     }
 }
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
     MP_THREAD_GIL_EXIT();
-    write(STDOUT_FILENO, str, len);
+    int ret = write(STDOUT_FILENO, str, len);
     MP_THREAD_GIL_ENTER();
+    return ret < 0 ? 0 : ret; // return the number of bytes written, so in case of an error in the syscall, return 0
 }
 
 void mp_hal_stdout_tx_strn_cooked(const char *str, size_t len) {
diff --git a/ports/zephyr/uart_core.c b/ports/zephyr/uart_core.c
index 1d37f2209..3f70cc0a1 100644
--- a/ports/zephyr/uart_core.c
+++ b/ports/zephyr/uart_core.c
@@ -44,7 +44,8 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 // Send string of given length
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    mp_uint_t ret = len;
     #ifdef CONFIG_CONSOLE_SUBSYS
     while (len--) {
         char c = *str++;
@@ -60,4 +61,5 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
         uart_poll_out(uart_console_dev, *str++);
     }
     #endif
+    return ret;
 }
diff --git a/py/mphal.h b/py/mphal.h
index 81cf50918..a4f222d0b 100644
--- a/py/mphal.h
+++ b/py/mphal.h
@@ -56,7 +56,7 @@ void mp_hal_stdout_tx_str(const char *str);
 #endif
 
 #ifndef mp_hal_stdout_tx_strn
-void mp_hal_stdout_tx_strn(const char *str, size_t len);
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len);
 #endif
 
 #ifndef mp_hal_stdout_tx_strn_cooked
diff --git a/shared/runtime/sys_stdio_mphal.c b/shared/runtime/sys_stdio_mphal.c
index 84ce5828e..b7a35a5cb 100644
--- a/shared/runtime/sys_stdio_mphal.c
+++ b/shared/runtime/sys_stdio_mphal.c
@@ -142,8 +142,7 @@ STATIC mp_uint_t stdio_buffer_read(mp_obj_t self_in, void *buf, mp_uint_t size,
 }
 
 STATIC mp_uint_t stdio_buffer_write(mp_obj_t self_in, const void *buf, mp_uint_t size, int *errcode) {
-    mp_hal_stdout_tx_strn(buf, size);
-    return size;
+    return mp_hal_stdout_tx_strn(buf, size);
 }
 
 STATIC const mp_stream_p_t stdio_buffer_obj_stream_p = {